In a vehicle navigation system, a map matching technique is used to display an accurate current position of a vehicle on a map. The current position is determined based on position information transmitted from the global positioning system (GPS) and matched by a map matching to a road on the map stored in a memory device.
When the vehicle is in a multistory or underground parking garage, it may take time until accurate map matching is performed. When a freeway and a local road (non-freeway) are parallel to each other, that is, for instance one above the other or side by side, the system may not recognize on which road the vehicle is currently located. The system may therefore not perform accurate map matching.
The same problem may occur when a elevated road and a ground-level road are in parallel to each other. The road on which the vehicle is currently located can be determined by detecting a slope of the elevated road. However, it requires an additional device such as an angle sensor.
In these cases, it takes for a while until accurate map matching is performed and therefore a current position cannot be searched accurately until then.